The Influence of Hypothermia on the Microscopical Picture of Different Organs in Rabbits

Abstract

Hypothermia was used some 20 years ago in the treatment of malignant tumours. During the last decade it has also been found useful in operations on the heart and on the brain. Methods now available for lowering the body temperature are regarded as safe. Nevertheless, some questions call for further investigation, such as: Does hypothermia produce morphological tissue changes?Microscopical changes after hypothermia have been observed in organs from various animals, but opinions differ in respect to both the extent and severity of the changes, and some authors even deny the occurrance of such changes.Artificial hypothermia, i.e. relatively rapid lowering of the general body temperature of anaesthetised human beings, found increasingly wide use after the fundamental investigations by Bigelow ( 1 ) . The microscopical changes described in these cases of hypothermia vary widely. Some authors, for example, found a n extracellular accumulation of fluid in different organs and degenerative changes and accumulation of inflammatory cells. Some investigators such as Sarajas ( 1 3 ) and Knocker ( 7 ) claim that these changes, a t least in dogs, are severe even if the organism is not cooled for any length of time, and even if the reduction in temperature is only small. On the other hand, other authors have not found any changes a t all or a t most slight changes (3, 6 ) . M A T E R I A L A N D M E T H O DNineteen full-grown rahhits were used. The animals anaesthetised with allylisohutylmalonylthiocarhamidesodium (Baytinal, Bayer) and afterwards cooled in a refrigerator ( 2 ) to $28" C. The temperature was maintained as steady as possihle at this level. Six rabbits were cooled for 48 hours, 2 for 34 and 2 for 38 and the remainder for 2-3 hours. Artificial respiration was not induced. The animals were killed immediately after the experiment. After careful gross inspection various organs (heart, liver, spleen, lungs and kidneys) were removed and fixed in 1 0 per cent formalin. 151